The invention relates to processes for surface modification of organic materials by exposure to actinic radiation while in contact with inorganic compounds, and bonded articles derived thereby.
Polymer surfaces have been modified by exposure to ultraviolet and/or visible radiation while such surfaces are in contact with selected compounds (i.e., modifiers). In some cases, those compounds are organic, and are selected for their ability to participate in electron transfer reactions with a polymer film and/or sensitizer. The resultant modified polymer surface typically has organic residues corresponding to the selected organic compounds covalently bonded to the polymer film. Such residues, being organic, may be colored and/or may have a tendency to oxidize when exposed to atmospheric oxygen causing a change in one or more properties (e.g., surface energy) of the surface over time. This may be especially important for polymer films, such as fluorine-containing polymer (i.e., fluoropolymer) films, that may not otherwise oxidize under ambient conditions.
It would be desirable to have processes, capable of permanently modifying the surface of a polymeric substrate, such that the surface is not prone to discoloration and/or oxidation for long periods of time.
Fluoropolymers are a commercially useful class of materials. Fluoropolymers include, for example, crosslinked fluoroelastomers and semi-crystalline or glassy fluoropolymers. Fluoropolymers are generally of high thermal stability and are particularly useful at high temperatures. They may also exhibit extreme toughness and flexibility at very low temperatures. Many of these fluoropolymers are almost totally insoluble in a wide variety of solvents and are generally chemically resistant. Some have extremely low dielectric loss and high dielectric strength, and may have unique non-adhesive and low friction properties. Fluoroelastomers, particularly the copolymers of vinylidene fluoride with other ethylenically unsaturated halogenated monomers, such as hexafluoropropylene, have particular utility in high temperature applications, such as seals, gaskets, and linings.
Surface modification of fluoropolymers using inorganic compounds may be relatively slow and or difficult to carry out (e.g., involving many process steps). It would be desirable to have processes for enhancing the rate of such processes and the ease with which they may be carried out.
Multi-layer constructions containing a fluoropolymer enjoy wide industrial application. Such constructions find utility, for example, in fuel line hoses and related containers and hoses or gaskets in the chemical processing field. Adhesion between the layers of a multi-layered article may need to meet various performance standards depending on the use of the finished article. However, it is often difficult to establish high bond strengths when one of the layers is a fluoropolymer, in part, because of the non-adhesive qualities of fluoropolymers.
It would be desirable to have methods for improving the strength of adhesive bonds to polymeric substrates.
The invention concerns novel processes for modifying the surface of a polymeric substrate. The modified polymeric substrates are useful in the manufacture of various articles.
In one aspect, the invention provides a process for modifying a polymeric substrate surface comprising:
a) providing a polymeric substrate having a surface;
b) contacting a photoreactive solution comprising solvent, at least one inorganic photochemical electron donor, and a cationic assistant with the polymeric substrate surface to form an interface; and
c) exposing the interface to actinic radiation.
In some embodiments, the inorganic photochemical electron donor comprises an element selected from the group consisting of sulfur, nitrogen, and phosphorus.
In some embodiments, the polymeric substrate comprises fluoropolymer, a polyimide, or a polyester.
In some embodiments, the process further comprises bonding the exposed interface to a second substrate, desirably a polymer film.
In another aspect, the invention provides a polymeric substrate having a surface prepared by a process for modifying a polymeric substrate surface comprising:
a) providing a polymeric substrate having a surface;
b) contacting a photoreactive solution comprising solvent, at least one inorganic photochemical electron donor, and a cationic assistant with the polymeric substrate surface to form an interface; and
c) exposing the interface to actinic radiation.
In another aspect, the invention provides a polymeric substrate having a surface preparable by a process for modifying a polymeric substrate surface comprising:
a) providing a polymeric substrate having a surface;
b) contacting a photoreactive solution comprising solvent, at least one inorganic photochemical electron donor, and a cationic assistant with the polymeric substrate surface to form an interface; and
c) exposing the interface to actinic radiation.
In another aspect, the invention provides a process for preparing a composite article comprising:
a) providing a polymeric substrate having a surface;
b) providing a second substrate having a surface;
c) coating a photoreactive solution comprising solvent, at least one inorganic photochemical electron donor, and a cationic assistant as a thin film onto the surface of the polymeric substrate to form a first interface;
d) contacting the surface of the second substrate with the coated photoreactive solution to form a second interface; and
e) simultaneously exposing both interfaces to actinic radiation sufficient to form a composite article.
In some embodiments, the second substrate is a polymer film.
In another aspect, the invention provides a composite article prepared by a process comprising:
a) providing a polymeric substrate having a surface;
b) providing a second substrate having a surface;
c) coating a photoreactive solution comprising solvent, at least one inorganic photochemical electron donor, and a cationic assistant as a thin film onto the surface of the polymeric substrate to form a first interface;
d) contacting the surface of the second substrate with the coated photoreactive solution to form a second interface; and
e) simultaneously exposing both interfaces to actinic radiation sufficient to form a composite article.
In some embodiments, the second substrate is a polymer film.
In another aspect, the invention provides a composite article preparable by a process comprising:
a) providing a polymeric substrate having a surface;
b) providing a second substrate having a surface;
c) coating a photoreactive solution comprising solvent, at least one inorganic photochemical electron donor, and a cationic assistant as a thin film onto the surface of the polymeric substrate to form a first interface;
d) contacting the surface of the second substrate with the coated photoreactive solution to form a second interface; and
e) simultaneously exposing both interfaces to actinic radiation sufficient to form a composite article.
In some embodiments, the second substrate is a polymer film.
Polymeric substrates, that are surface-modified according to various aspects of the invention, typically exhibit improved adhesion when bonded to another solid substrate and are useful for preparation of various composite articles. Also, polymeric substrates having surfaces modified according to various aspects of the invention may be used to bind or absorb various species, such as biologically active molecules, electrolessly plated metal films, adhesives (including pressure-sensitive adhesives), and the like. Since by masking a portion of the actinic radiation the methods of the invention may be used to produce patterns in an image-wise manner on the polymeric substrate, they may be useful in printing processes, and in the manufacture of electronic articles.
As used in this application:
xe2x80x9cactinic radiationxe2x80x9d means light having a wavelength of from about 200 nanometers to about 400 nanometers;
xe2x80x9ccuredxe2x80x9d means covalently cross-linked;
xe2x80x9celastomerxe2x80x9d means a material that has resiliency properties similar to those of rubber; in particular, the term elastomer reflects the property of the material to undergo a substantial stress elongation and then return to substantially its original dimensions upon release of the stress elongating the elastomer;
xe2x80x9cinorganicxe2x80x9d means having neither a Cxe2x80x94H bond, nor a carbon to carbon multiple bond, nor a tetracoordinate carbon atom; in embodiments of the invention in which an inorganic photochemical electron donor is ionic, the term xe2x80x9cinorganicxe2x80x9d refers to the anionic portion of the ionic compound only, that is, the cationic portion of the ionic compound, which is present of necessity to maintain the overall charge balance, may therefore be organic as in the case of, for example, tetraalkylammonium thiocyanate;
xe2x80x9cnon-volatile saltxe2x80x9d refers to a salt consisting of a cation and anion, wherein the cation, and any corresponding conjugate base that may exist in equilibrium with the cation, have a vapor pressure of less than about 10 millipascals at 25xc2x0 C.;
xe2x80x9corganicxe2x80x9d means not inorganic as defined herein;
xe2x80x9cphotochemical electron donorxe2x80x9d refers to a compound that undergoes photochemical one-electron oxidation;
xe2x80x9csolublexe2x80x9d means dissolvable in the chosen solvent at concentrations exceeding about 0.001 mole per liter;
xe2x80x9cthermoplasticxe2x80x9d refers to a polymer that softens and flows when exposed to heat and solidifies when cooled to room temperature; and
xe2x80x9cthermosetxe2x80x9d refers to a polymeric material, optionally containing a curing agent, that solidifies or xe2x80x9csetsxe2x80x9d irreversibly with respect to heat when cured.